EP2722278B1 - Ion propulsion systems comprising thruster grid clear circuits and methods to clear thruster grids - Google Patents
Ion propulsion systems comprising thruster grid clear circuits and methods to clear thruster grids Download PDFInfo
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- EP2722278B1 EP2722278B1 EP13187409.1A EP13187409A EP2722278B1 EP 2722278 B1 EP2722278 B1 EP 2722278B1 EP 13187409 A EP13187409 A EP 13187409A EP 2722278 B1 EP2722278 B1 EP 2722278B1
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- 238000000034 method Methods 0.000 title claims description 83
- 230000008569 process Effects 0.000 claims description 50
- 230000004044 response Effects 0.000 claims description 6
- 150000002500 ions Chemical class 0.000 description 27
- 238000004519 manufacturing process Methods 0.000 description 9
- 238000010586 diagram Methods 0.000 description 7
- 239000000463 material Substances 0.000 description 4
- 238000012423 maintenance Methods 0.000 description 3
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 2
- 230000008901 benefit Effects 0.000 description 2
- 238000013461 design Methods 0.000 description 2
- 230000005669 field effect Effects 0.000 description 2
- 230000010354 integration Effects 0.000 description 2
- 229910052750 molybdenum Inorganic materials 0.000 description 2
- 239000011733 molybdenum Substances 0.000 description 2
- 239000003380 propellant Substances 0.000 description 2
- 230000009467 reduction Effects 0.000 description 2
- 230000001133 acceleration Effects 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000011835 investigation Methods 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 229910044991 metal oxide Inorganic materials 0.000 description 1
- 150000004706 metal oxides Chemical class 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
- 230000008520 organization Effects 0.000 description 1
- 230000037361 pathway Effects 0.000 description 1
- 238000009419 refurbishment Methods 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- 229910052724 xenon Inorganic materials 0.000 description 1
- FHNFHKCVQCLJFQ-UHFFFAOYSA-N xenon atom Chemical compound [Xe] FHNFHKCVQCLJFQ-UHFFFAOYSA-N 0.000 description 1
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Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B64—AIRCRAFT; AVIATION; COSMONAUTICS
- B64G—COSMONAUTICS; VEHICLES OR EQUIPMENT THEREFOR
- B64G1/00—Cosmonautic vehicles
- B64G1/22—Parts of, or equipment specially adapted for fitting in or to, cosmonautic vehicles
- B64G1/40—Arrangements or adaptations of propulsion systems
- B64G1/411—Electric propulsion
- B64G1/413—Ion or plasma engines
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B08—CLEANING
- B08B—CLEANING IN GENERAL; PREVENTION OF FOULING IN GENERAL
- B08B7/00—Cleaning by methods not provided for in a single other subclass or a single group in this subclass
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
- F03H—PRODUCING A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
- F03H1/00—Using plasma to produce a reactive propulsive thrust
- F03H1/0037—Electrostatic ion thrusters
- F03H1/0043—Electrostatic ion thrusters characterised by the acceleration grid
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B64—AIRCRAFT; AVIATION; COSMONAUTICS
- B64G—COSMONAUTICS; VEHICLES OR EQUIPMENT THEREFOR
- B64G1/00—Cosmonautic vehicles
- B64G1/22—Parts of, or equipment specially adapted for fitting in or to, cosmonautic vehicles
- B64G1/40—Arrangements or adaptations of propulsion systems
- B64G1/405—Ion or plasma engines
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
Definitions
- Ion thrusters are currently used for spacecraft control on some communications satellites. Some existing systems operate by ionizing xenon gas and accelerating it across two or three charged molybdenum grids. As the ions pass through these grids, small amounts of molybdenum are sputtered off to deposit on the downstream grids. Over time, these deposits can grow large enough to flake off and cause a short circuit between the grids, shutting down the thruster. When this occurs, the thruster must be turned off so that the grids can be cleared to remove the short circuit. Grid clear circuitry is employed to apply energy through the short, causing the material to be burned off.
- FIG. 1 is a schematic diagram of a contaminated ion propulsion grid within an ion thruster.
- ionized gas 102 is accelerated across two or more charged grids 104.
- deposits can accumulate on the grids 104 to a point where a short circuit 106 is created, which reduces or eliminates the effectiveness of the thruster.
- Prior art grid clear circuits employ a dropping resistor 110 coupled to a voltage source 108 (e.g., the spacecraft bus voltage) to clear the grids 104.
- the voltage source 108 is applied (through the dropping resistor 110) to the shorted grids 104.
- additional benefits or advantages e.g., reduce operating or maintenance costs, increase thruster service life, increase grid service life, reduce energy requirements, for example, for clearing a grid, but still effectively reduce or remove contamination on grid surfaces or grid systems.
- an ion propulsion system comprising: a plurality of adjacent ion propulsion system thruster grids including outer grids; a low voltage grid clear circuit configured to apply first energy to the outer grids at a first voltage; and a high voltage grid clear circuit configured to apply second energy to the outer grids at a second voltage higher than the first voltage.
- a method for operating the ion propulsion system of the above first aspect comprising: detecting a first grid clear process comprising applying the first voltage to the outer grids; and applying a second grid clear process comprising applying the second voltage higher than the first voltage to the outer grids.
- Example ion propulsion systems, thruster grid clear circuits, and methods to clear thruster grids are disclosed below.
- the example ion propulsion systems, thruster grid clear circuits, and methods to clear thruster grids are able to clear a wider variety of short circuit conditions caused by deposits on thruster grids. For example, some types of short circuit conditions appear at relatively high voltages but do not appear at lower voltages that have been used in the past to clear such short circuit conditions.
- an ion propulsion system includes a low-voltage grid clear circuit and a high-voltage grid clear circuit.
- the example low-voltage grid clear circuit is capable of applying higher electrical currents at lower voltages (e.g., 100V) to remove deposits that cause short circuits in a thruster grid.
- the high-voltage grid clear circuit applies a high-voltage signal to initiate an arc, which enables the low-voltage grid clear circuit to apply a higher current to clear the deposits.
- the high-voltage grid clear circuit monitors the low-voltage grid clear circuit to determine whether the low-voltage grid clear process is effective at clearing (e.g., eliminating) the short circuit condition. If the high-voltage grid clear circuit determines that the low-voltage grid clear process does not clear the short circuit condition, the high-voltage grid clear circuit applies a high-voltage grid clear process to the thruster grid.
- the high-voltage grid clear process includes applying a substantially higher voltage (e.g., 1000V) to the thruster grid.
- the high-voltage grid clear process may cause an arc to occur between a first grid electrically coupled to the low-voltage grid clear circuit and a second grid electrically coupled to a reference voltage.
- the induced arc between the grids occurs between deposits located on the respective grids.
- the induced arc creates a low-resistance plasma path between the first and second grids (e.g., between the deposits).
- the low-resistance path enables the low-voltage grid clear process to direct higher currents through the deposits, thereby enabling the low-voltage grid clear circuit to clear the deposits (e.g., clear the short circuit condition).
- any pair of adjacent thruster grids in an ion propulsion thruster may be cleared of a short-circuit condition using the low-voltage grid clear process and the high-voltage grid clear process.
- an ion propulsion thruster includes three thruster grids, in which a center one of the grids is located between and, thus, is adjacent the other two grids.
- Short circuits occurring between the center grid and a first one of the outside grids may be cleared by applying the low voltage grid clear process (e.g., via a low-voltage grid clear circuit) and the high voltage grid clear process (e.g., via a high-voltage grid clear circuit) to the center grid while the first outside grid is connected to a reference and/or by applying the low voltage grid clear process and the high voltage grid clear process to the first outside grid while the center grid is connected to a reference.
- the low voltage grid clear process e.g., via a low-voltage grid clear circuit
- the high voltage grid clear process e.g., via a high-voltage grid clear circuit
- short circuits between the center grid and a second one of the outside grids may be cleared by applying the low voltage grid clear process and the high voltage grid clear process to the center grid while the second outside grid is connected to a reference and/or by applying the low voltage grid clear process and the high voltage grid clear process to the second outside grid while the center grid is connected to a reference.
- short circuits between both the center grid and the first outside grid, and the center grid and the second outside grid can be cleared by applying the low voltage grid clear process and the high voltage grid clear process to the center grid while the outside grids are connected to a reference and/or by applying the low voltage grid clear process and the high voltage grid clear process to the outside grids while the center grid is connected to a reference.
- FIG. 2 is a block diagram of an example ion propulsion system 200 including grid clear circuits.
- the example ion propulsion system 200 of FIG. 2 may be used to provide propulsion for a platform such as a spacecraft.
- the ion propulsion system 200 of FIG. 2 includes power supplies 202, a thruster 204, thruster grids 206, 208, 210, a low-voltage grid clear circuit 212, and a high-voltage grid clear circuit 214.
- the example power supplies 202 provide electrical energy to the thruster 204 and the thruster grids 206-210 to enable the thruster 204 to provide thrust.
- the example power supplies 202 may provide electrical energy at multiple voltages and/or currents to fulfill specific needs of the thruster 204 and/or the grids 206-210.
- the example thruster 204 includes propellant 216 and electrodes 218.
- the propellant 216 is transformed into ions by generation of electrons by the electrodes 218.
- the example thruster grids 206-210 are electrically charged to accelerate the resulting ions to produce thrust.
- the example grid 206 is a screen grid
- the example grid 208 is an acceleration grid
- the example grid 210 is a deceleration grid.
- the deceleration grid 210 is omitted.
- additional grids are included. Over time, material deposits may build between adjacent ones of the grids 206-210.
- these deposits can reduce the distance between adjacent ones of the grids 206, 208 and 208, 210 such that the high voltages between the adjacent grids 206, 208 or 208, 210 bridges the gap(s) and results in a short circuit, which reduces the effectiveness of the thruster 204 or renders the thruster 204 inoperable.
- the power supplies 202 When the power supplies 202 detect a short circuit, the power supplies 202 (or another controller) signals the low-voltage grid clear circuit 212 to attempt to clear the short circuit condition.
- the example low-voltage grid clear circuit 212 applies a low-voltage, high-current (e.g., 100 V) electrical signal to the outer grids 206, 210.
- the example high-voltage grid clear circuit 214 applies a high-voltage grid clear process to the outer grids 206, 210.
- the high-voltage grid clear circuit 214 provides additional (e.g., second) energy to enable the low-voltage grid clear process to clear the short circuit condition.
- the high-voltage grid clear circuit 214 monitors the low-voltage grid clear circuit 212 to determine whether the short circuit condition is cleared. If the high-voltage grid clear circuit 214 determines that the low-voltage grid clear circuit 212 has failed to clear the short circuit, the example high-voltage grid clear circuit 214 applies a high-voltage electrical signal (e.g., 1000 V) to the outer grids 206, 210.
- the high-voltage electrical signal may be current limited to avoid damaging the grids 206-210 and/or the thruster 204.
- the inner grid 208 remains coupled to a reference voltage.
- the high-voltage grid clear circuit 214 produces an arc over the gap between the adjacent grids 206, 208 or 208, 210.
- the arc creates a low-resistance plasma path between the adjacent grids 206, 208 or 208, 210, which can be traversed by the low-voltage grid clear process.
- the example low-voltage grid clear circuit 212 can be used in conjunction with the high-voltage grid clear circuit 214 to direct larger amounts of current through the deposits to clear them.
- the high-voltage grid clear circuit 214 detects that the low-voltage grid clear circuit 212 is directing current (e.g., to clear the deposits), the high-voltage grid clear circuit 214 stops applying the high-voltage signal. If the low-voltage grid clear process exhibits additional reductions in current flow, the example high-voltage grid clear circuit 214 is re-enabled and re-establishes the arc path. In the example of FIG. 2 , the low-voltage grid clear process and, as necessary, the high-voltage grid clear process continue until a certain time has elapsed and/or until the grid clear processes have applied a threshold amount of energy to the grids 206-210.
- the example low-voltage grid clear circuit 212 and the high-voltage grid clear circuit 214 stop directing current to the grids 206-210 and the operation of the thruster 204 may be resumed. In some examples, success in clearing the deposits is not known until a restart of the thruster 204 is attempted. If the deposit is not successfully cleared, the example system 200 may initiate additional attempts at clearing the short circuit condition using the grid clear circuits 212, 214.
- FIG. 3 is a more detailed schematic diagram of the example grid clear circuits 212, 214 of FIG. 2 .
- the example low-voltage grid clear circuit 212 is coupled to an electrical bus 302 and to a grid clear signal 304 (e.g., from the power supplies 202 of FIG. 2 , from a controller, or from other source(s)).
- the bus 302 provides electrical energy that is used by the grid clear circuits 212, 214 to apply low-voltage energy and high-voltage energy, respectively, to clear short circuit conditions in the grids 206-210.
- the low-voltage grid clear circuit 212 of FIG. 3 includes switching elements 306, 308 (e.g., metal oxide semiconductor field effect transistors (MOSFETs), junction field effect transistors (JFETs), bipolar junction transistors (BJTs), electromechanical switching elements, etc.) to control the application of the electrical energy to the grids 206-210.
- the example switching elements 306, 308 are controlled by the grid clear signal 304.
- the switching elements 306, 308 are electrically closed (i.e., conducting current)
- an electrical signal is applied to the outer grids 206, 210 via the bus 302.
- current may flow from the bus 302 through the grid(s) 206, 210 and to the grid 208.
- the example low-voltage grid clear circuit 212 of FIG. 3 further includes current limiting and/or current sense resistors 310, 312.
- current is flowing to the grid 206 (or to the grid 210)
- a substantial voltage drop occurs across terminals of the resistor(s) 310 (or the resistor(s) 312).
- the switching elements 306, 308 are closed and current is unable to flow through the grids 206-210 (e.g., because the low-voltage grid clear process is unable to bridge a gap between adjacent grids 206, 208 and 208, 210)
- the voltage drops over the resistors 310, 312 is relatively small or substantially equal to zero.
- the example high-voltage grid clear circuit 214 of FIG. 3 includes a high voltage controller 314, a high voltage generator 316, and a switching element 318.
- the example high voltage controller 314 monitors the low-voltage grid clear circuit 212 to determine whether a short circuit condition exists and to determine whether the low-voltage grid clear process is effective or has failed to clear the short circuit condition.
- the high-voltage controller 314 of FIG. 3 monitors voltages at first nodes 320, 322 (e.g., coupled to first terminals of the resistors 310, 312). When the voltages at the first nodes 320, 322 have voltages higher than a threshold, the example controller 314 determines that a short condition has occurred (e.g., because the switching elements 306, 308 have been closed).
- the example high voltage controller 314 further detects whether the low-voltage grid clear process (e.g., performed by the low-voltage grid clear circuit 212) has failed to clear the short circuit condition. For example, in addition to monitoring the node voltages at the nodes 320, 322, the example high voltage controller 314 monitors node voltages at nodes 324, 326 (e.g., on the opposite ends of the resistors 310, 312 from the nodes 320, 322). If a difference in voltage across a resistor 310, 312 (e.g., between the nodes 320 and 324 or nodes 322 and 326) is greater than a threshold, the example high voltage controller 314 determines that current is being applied to the respective grid(s) 206-210. In contrast, if the difference in voltage is less than a threshold, the example high voltage controller 314 may determine that the low-voltage grid clear process cannot bridge a gap between the grids 206-210 and, thus, is failing to clear the short circuit condition.
- the example high voltage controller 314 In response to detecting a failure to clear the short circuit condition, the example high voltage controller 314 provides a signal to electrically close the switching element 318. As a result, the high voltage generator 316 generates a high-voltage signal (e.g., 1000 V) and applies the high-voltage signal to the grids 206, 210. If successful, the high-voltage signal creates an arc between the grid(s) 206, 210 and the grid 208 to provide the low-voltage grid clear circuit 212 with a low-resistance path with which to apply energy to the grids 206, 210.
- a high-voltage signal e.g. 1000 V
- the example high voltage controller 314 detects the reduction in voltage at the node(s) 324, 326 and electrically opens the example switching element 318 to stop applying the high voltage to the grids 206, 210. If the low-voltage grid clear circuit 212 is unable to maintain the low resistance pathway and the current flow stops, the example high voltage controller 314 again detects the increase in voltage and re-applies the high voltage to the grids 206, 210. This example process may iterate until, for example, the short circuit condition is cleared and/or until the grid clear signal 304 is removed.
- the example high voltage controller 314 may include logic circuits and/or other control circuitry. In some examples, the high voltage controller 314 is implemented in other logic in a platform that includes the ion propulsion system 200 of FIG. 2 (e.g., in a spacecraft).
- FIG. 4 is a flowchart representative of an example method 400 to clear a short condition in a thruster grid.
- the example method 400 may be implemented using the low-voltage grid clear circuit 212 and the high-voltage grid clear circuit 214 of FIGS. 2 and 3 .
- the method 400 is invoked when a short circuit condition is detected in a thruster grid of an ion propulsion system such as the system 200 of FIG. 2 .
- the example method 400 of FIG. 4 begins by applying first energy having a first voltage (e.g., 100 V) to a grid (e.g., the grids 206, 210 of FIG. 3 ) (block 402).
- a grid e.g., the grids 206, 210 of FIG. 3
- the example high-voltage grid clear circuit 214 (e.g., via the high voltage controller 314) measures a first node voltage (block 404).
- the first node voltage may be measured, for example, at the node 320 or at the node 322.
- the high-voltage grid clear circuit 214 (e.g., via the high voltage controller 314) also measures a second node voltage (block 406).
- the second node voltage may be measured, for example, at the node 324 or the node 326 (e.g., the one of the nodes 324, 326 corresponding to (e.g., opposite) the node 320, 322 from which the first node voltage was measured).
- the example high voltage controller 314 determines whether a difference between the first node voltage and the second node voltage is less than a threshold (block 408). If the difference is less than the threshold (block 408), the example high voltage controller 314 detects a failure of the first energy (e.g., from the low-voltage grid clear circuit 212) to clear the grid short condition (block 410).
- the high-voltage grid clear circuit 214 applies second energy having a second voltage to the grid(s) 206, 210 (block 412). For example, the high voltage controller 314 may close the switching element 318 to cause the high voltage generator 316 to begin applying the high voltage to the grid(s) 206, 210.
- the example high-voltage grid clear circuit 214 (e.g., via the high voltage controller 314) measures the first node voltage (e.g., at the same node 320, 322 as the first node voltage was measured in block 404) (block 414).
- the high-voltage grid clear circuit 214 (e.g., via the high voltage controller 314) also measures the second node voltage (e.g., at the same node 324, 326 as the second node voltage was measured in block 406) (block 416).
- the example high voltage controller 314 determines whether a difference between the first node voltage and the second node voltage is less than a threshold (block 418).
- the example high voltage controller 314 determines whether a threshold time has elapsed (block 420). For example, the high-voltage grid clear process and/or the low-voltage grid clear process may be time-limited to avoid damaging the thruster grids 206-210. If the threshold time has not elapsed (block 420), control returns to block 412 to continue applying the second energy to the grid(s) 206, 210. If the difference between the first and second node voltages is not less than the threshold (block 418), the example high-voltage grid clear circuit 214 stops applying the second energy (block 422).
- the example low-voltage grid clear circuit 212 determines whether to stop applying the first energy (block 424). For example, the low-voltage grid clear circuit 212 may detect the state or value of the grid clear signal 304. If the low-voltage grid clear circuit 212 is to continue applying the first energy (block 424), control returns to block 402. If the low-voltage grid clear circuit 212 stops applying the first energy (block 424) or if the threshold time has elapsed (block 420), the example method 400 ends. In an example in which the threshold time elapses prior to the high-voltage grid clear circuit 214 stopping the second energy, determining the threshold time has elapsed includes stopping both the first and second energies (e.g., via the grid clear signal 304).
- Examples of the disclosure may be described in the context of a platform manufacturing and service method 500 as shown in FIG. 5 and a platform 600, such as spacecraft, as shown in FIG. 6 .
- the example method 500 may include specification and design (block 502) of the platform 600 (e.g., a spacecraft), such as the placement(s) and/or design(s) of the example power supplies 202, the example thruster 204, the example low-voltage grid clear circuit 212, and/or the high-voltage grid clear circuit 214.
- Preproduction may further include material procurement (block 504).
- component and subassembly manufacturing (block 506) and system integration (block 508) of the platform 600 e.g., a spacecraft) takes place.
- the example power supplies 202, the example thruster 204, the example low-voltage grid clear circuit 212, and/or the high-voltage grid clear circuit 214 may be attached (e.g., affixed) to structural locations. Thereafter, the platform 600 (e.g., a spacecraft) may go through certification and delivery (block 510) in order to be placed in service (block 512). While in service by a customer, the platform 600 (e.g., a spacecraft) is scheduled for routine maintenance and service (block 514), which may also include modification, reconfiguration, refurbishment, etc.
- routine maintenance and service block 514
- a system integrator may include without limitation any number of platform (e.g., aircraft) manufacturers and major-system subcontractors;
- a third party may include without limitation any number of venders, subcontractors, and suppliers; and
- an operator may be an airline, leasing company, military entity, service organization, and so on.
- the platform 600 (e.g., spacecraft) produced by example method 500 may include a frame 602 with a plurality of systems 604 and an interior 606.
- high-level systems 604 include one or more of a propulsion system 608, an electrical system 610, a hydraulic system 612, and an environmental system 614.
- the example methods and apparatus disclosed herein may be integrated into the example systems 608-614 to provide clearing of grid short circuits. Any number of other systems may be included.
- Apparatus and methods embodied herein may be employed during any one or more of the stages of the production and service method 500.
- components or subassemblies corresponding to production process 506 may be fabricated or manufactured in a manner similar to components or subassemblies produced while the platform 600 (e.g., spacecraft) is in service 512.
- one or more apparatus embodiments, method embodiments, or a combination thereof may be implemented during the production stages 506 and 508, for example, by substantially expediting assembly of or reducing the cost of a platform 600 (e.g., spacecraft).
- one or more of apparatus embodiments, method embodiments, or a combination thereof may be utilized while the platform 600 (e.g., spacecraft) is in service 512, for example and without limitation, to maintenance and service 514.
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Description
- Ion thrusters are currently used for spacecraft control on some communications satellites. Some existing systems operate by ionizing xenon gas and accelerating it across two or three charged molybdenum grids. As the ions pass through these grids, small amounts of molybdenum are sputtered off to deposit on the downstream grids. Over time, these deposits can grow large enough to flake off and cause a short circuit between the grids, shutting down the thruster. When this occurs, the thruster must be turned off so that the grids can be cleared to remove the short circuit. Grid clear circuitry is employed to apply energy through the short, causing the material to be burned off.
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FIG. 1 is a schematic diagram of a contaminated ion propulsion grid within an ion thruster. When the thruster is operating, ionizedgas 102 is accelerated across two or morecharged grids 104. However, deposits can accumulate on thegrids 104 to a point where ashort circuit 106 is created, which reduces or eliminates the effectiveness of the thruster. - Prior art grid clear circuits employ a dropping
resistor 110 coupled to a voltage source 108 (e.g., the spacecraft bus voltage) to clear thegrids 104. Thevoltage source 108 is applied (through the dropping resistor 110) to the shortedgrids 104. However, there is still a need for other grid clearing processes and circuitry that would provide improvements over prior art systems and provide additional benefits or advantages (e.g., reduce operating or maintenance costs, increase thruster service life, increase grid service life, reduce energy requirements, for example, for clearing a grid, but still effectively reduce or remove contamination on grid surfaces or grid systems. - The article "Experimental and Theoretical Analysis for Designing a Grid Clearing System for the NEXT Ion Propulsion System" (XP055250526) reports on screens to accelerator grid shorts have occurs on two NASA spacecraft using ion propulsion systems. This resulted in loss of thrusting capabilities on one of the spacecraft. Since grid shorts are a potential life limiting mechanism for ion thrusters, grid clear circuits have been implemented to provide a method of clearing the fault. A general methodology that can be used to deal with a grid short if it arises during a mission is discussed; this includes examining a variety of techniques including use of a grid clear circuit to clear the short. In addition, experimental and theoretical investigation of a potential grid clear circuit for the NEXT ion thruster has is presented. This includes information on the size and types of material that might cause a grid short. The parameters that influence the ability to clear a short are discussed and experimental data obtained while investigating these parameters is presented.
- According to a first aspect it is disclosed an ion propulsion system, comprising: a plurality of adjacent ion propulsion system thruster grids including outer grids; a low voltage grid clear circuit configured to apply first energy to the outer grids at a first voltage; and a high voltage grid clear circuit configured to apply second energy to the outer grids at a second voltage higher than the first voltage.
- According to another aspect it is disclosed a method for operating the ion propulsion system of the above first aspect, comprising: detecting a first grid clear process comprising applying the first voltage to the outer grids; and applying a second grid clear process comprising applying the second voltage higher than the first voltage to the outer grids.
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FIG. 1 is a schematic diagram of a contaminated ion propulsion grid within an ion thruster. -
FIG. 2 is a block diagram of an example ion propulsion system including grid clear circuits. -
FIG. 3 is a more detailed schematic diagram of the example grid clear circuits ofFIG. 2 . -
FIG. 4 is a flowchart illustrating an example method to clear a thruster grid short circuit condition. -
FIG. 5 is a flowchart of platform production and service methodology. -
FIG. 6 is a block diagram of a platform. - Example ion propulsion systems, thruster grid clear circuits, and methods to clear thruster grids are disclosed below. In contrast to present grid clear circuits, the example ion propulsion systems, thruster grid clear circuits, and methods to clear thruster grids are able to clear a wider variety of short circuit conditions caused by deposits on thruster grids. For example, some types of short circuit conditions appear at relatively high voltages but do not appear at lower voltages that have been used in the past to clear such short circuit conditions.
- In some examples, an ion propulsion system includes a low-voltage grid clear circuit and a high-voltage grid clear circuit. The example low-voltage grid clear circuit is capable of applying higher electrical currents at lower voltages (e.g., 100V) to remove deposits that cause short circuits in a thruster grid. The high-voltage grid clear circuit applies a high-voltage signal to initiate an arc, which enables the low-voltage grid clear circuit to apply a higher current to clear the deposits. In some examples, the high-voltage grid clear circuit monitors the low-voltage grid clear circuit to determine whether the low-voltage grid clear process is effective at clearing (e.g., eliminating) the short circuit condition. If the high-voltage grid clear circuit determines that the low-voltage grid clear process does not clear the short circuit condition, the high-voltage grid clear circuit applies a high-voltage grid clear process to the thruster grid.
- In some examples, the high-voltage grid clear process includes applying a substantially higher voltage (e.g., 1000V) to the thruster grid. The high-voltage grid clear process may cause an arc to occur between a first grid electrically coupled to the low-voltage grid clear circuit and a second grid electrically coupled to a reference voltage. In some examples, the induced arc between the grids occurs between deposits located on the respective grids. The induced arc creates a low-resistance plasma path between the first and second grids (e.g., between the deposits). The low-resistance path enables the low-voltage grid clear process to direct higher currents through the deposits, thereby enabling the low-voltage grid clear circuit to clear the deposits (e.g., clear the short circuit condition).
- In some examples, any pair of adjacent thruster grids in an ion propulsion thruster may be cleared of a short-circuit condition using the low-voltage grid clear process and the high-voltage grid clear process. In an example, an ion propulsion thruster includes three thruster grids, in which a center one of the grids is located between and, thus, is adjacent the other two grids. Short circuits occurring between the center grid and a first one of the outside grids may be cleared by applying the low voltage grid clear process (e.g., via a low-voltage grid clear circuit) and the high voltage grid clear process (e.g., via a high-voltage grid clear circuit) to the center grid while the first outside grid is connected to a reference and/or by applying the low voltage grid clear process and the high voltage grid clear process to the first outside grid while the center grid is connected to a reference.
- Similarly, short circuits between the center grid and a second one of the outside grids may be cleared by applying the low voltage grid clear process and the high voltage grid clear process to the center grid while the second outside grid is connected to a reference and/or by applying the low voltage grid clear process and the high voltage grid clear process to the second outside grid while the center grid is connected to a reference.
- In some examples, short circuits between both the center grid and the first outside grid, and the center grid and the second outside grid, can be cleared by applying the low voltage grid clear process and the high voltage grid clear process to the center grid while the outside grids are connected to a reference and/or by applying the low voltage grid clear process and the high voltage grid clear process to the outside grids while the center grid is connected to a reference.
-
FIG. 2 is a block diagram of an exampleion propulsion system 200 including grid clear circuits. The exampleion propulsion system 200 ofFIG. 2 may be used to provide propulsion for a platform such as a spacecraft. Theion propulsion system 200 ofFIG. 2 includespower supplies 202, athruster 204,thruster grids clear circuit 212, and a high-voltage gridclear circuit 214. - The
example power supplies 202 provide electrical energy to thethruster 204 and the thruster grids 206-210 to enable thethruster 204 to provide thrust. Theexample power supplies 202 may provide electrical energy at multiple voltages and/or currents to fulfill specific needs of thethruster 204 and/or the grids 206-210. - The
example thruster 204 includespropellant 216 andelectrodes 218. Thepropellant 216 is transformed into ions by generation of electrons by theelectrodes 218. The example thruster grids 206-210 are electrically charged to accelerate the resulting ions to produce thrust. Theexample grid 206 is a screen grid, theexample grid 208 is an acceleration grid, and theexample grid 210 is a deceleration grid. In some examples, thedeceleration grid 210 is omitted. In some other examples, additional grids are included. Over time, material deposits may build between adjacent ones of the grids 206-210. Eventually, these deposits can reduce the distance between adjacent ones of thegrids adjacent grids thruster 204 or renders thethruster 204 inoperable. - When the
power supplies 202 detect a short circuit, the power supplies 202 (or another controller) signals the low-voltage gridclear circuit 212 to attempt to clear the short circuit condition. The example low-voltage gridclear circuit 212 applies a low-voltage, high-current (e.g., 100 V) electrical signal to theouter grids clear circuit 214 applies a high-voltage grid clear process to theouter grids adjacent grids clear circuit 214 provides additional (e.g., second) energy to enable the low-voltage grid clear process to clear the short circuit condition. - In the example of
FIG. 2 , the high-voltage gridclear circuit 214 monitors the low-voltage gridclear circuit 212 to determine whether the short circuit condition is cleared. If the high-voltage gridclear circuit 214 determines that the low-voltage gridclear circuit 212 has failed to clear the short circuit, the example high-voltage gridclear circuit 214 applies a high-voltage electrical signal (e.g., 1000 V) to theouter grids thruster 204. Theinner grid 208 remains coupled to a reference voltage. - The high-voltage grid
clear circuit 214 produces an arc over the gap between theadjacent grids adjacent grids clear circuit 212 can be used in conjunction with the high-voltage gridclear circuit 214 to direct larger amounts of current through the deposits to clear them. - When the high-voltage grid
clear circuit 214 detects that the low-voltage gridclear circuit 212 is directing current (e.g., to clear the deposits), the high-voltage gridclear circuit 214 stops applying the high-voltage signal. If the low-voltage grid clear process exhibits additional reductions in current flow, the example high-voltage gridclear circuit 214 is re-enabled and re-establishes the arc path. In the example ofFIG. 2 , the low-voltage grid clear process and, as necessary, the high-voltage grid clear process continue until a certain time has elapsed and/or until the grid clear processes have applied a threshold amount of energy to the grids 206-210. - In cases in which the deposits are successfully cleared, the example low-voltage grid
clear circuit 212 and the high-voltage gridclear circuit 214 stop directing current to the grids 206-210 and the operation of thethruster 204 may be resumed. In some examples, success in clearing the deposits is not known until a restart of thethruster 204 is attempted. If the deposit is not successfully cleared, theexample system 200 may initiate additional attempts at clearing the short circuit condition using the gridclear circuits -
FIG. 3 is a more detailed schematic diagram of the example gridclear circuits FIG. 2 . The example low-voltage gridclear circuit 212 is coupled to anelectrical bus 302 and to a grid clear signal 304 (e.g., from the power supplies 202 ofFIG. 2 , from a controller, or from other source(s)). Thebus 302 provides electrical energy that is used by the gridclear circuits - The low-voltage grid
clear circuit 212 ofFIG. 3 includes switchingelements 306, 308 (e.g., metal oxide semiconductor field effect transistors (MOSFETs), junction field effect transistors (JFETs), bipolar junction transistors (BJTs), electromechanical switching elements, etc.) to control the application of the electrical energy to the grids 206-210. Theexample switching elements clear signal 304. When the switchingelements outer grids bus 302. When a short circuit condition exists, current may flow from thebus 302 through the grid(s) 206, 210 and to thegrid 208. - The example low-voltage grid
clear circuit 212 ofFIG. 3 further includes current limiting and/orcurrent sense resistors elements adjacent grids resistors - The example high-voltage grid
clear circuit 214 ofFIG. 3 includes a high voltage controller 314, ahigh voltage generator 316, and aswitching element 318. The example high voltage controller 314 monitors the low-voltage gridclear circuit 212 to determine whether a short circuit condition exists and to determine whether the low-voltage grid clear process is effective or has failed to clear the short circuit condition. For example, the high-voltage controller 314 ofFIG. 3 monitors voltages atfirst nodes 320, 322 (e.g., coupled to first terminals of theresistors 310, 312). When the voltages at thefirst nodes elements - The example high voltage controller 314 further detects whether the low-voltage grid clear process (e.g., performed by the low-voltage grid clear circuit 212) has failed to clear the short circuit condition. For example, in addition to monitoring the node voltages at the
nodes nodes 324, 326 (e.g., on the opposite ends of theresistors nodes 320, 322). If a difference in voltage across aresistor 310, 312 (e.g., between thenodes nodes 322 and 326) is greater than a threshold, the example high voltage controller 314 determines that current is being applied to the respective grid(s) 206-210. In contrast, if the difference in voltage is less than a threshold, the example high voltage controller 314 may determine that the low-voltage grid clear process cannot bridge a gap between the grids 206-210 and, thus, is failing to clear the short circuit condition. - In response to detecting a failure to clear the short circuit condition, the example high voltage controller 314 provides a signal to electrically close the switching
element 318. As a result, thehigh voltage generator 316 generates a high-voltage signal (e.g., 1000 V) and applies the high-voltage signal to thegrids grid 208 to provide the low-voltage gridclear circuit 212 with a low-resistance path with which to apply energy to thegrids - When the low-voltage grid
clear circuit 212 begins directing current to the grid(s) 206, 210, the voltage(s) at the node(s) 324, 326 decreases. The example high voltage controller 314 detects the reduction in voltage at the node(s) 324, 326 and electrically opens theexample switching element 318 to stop applying the high voltage to thegrids clear circuit 212 is unable to maintain the low resistance pathway and the current flow stops, the example high voltage controller 314 again detects the increase in voltage and re-applies the high voltage to thegrids clear signal 304 is removed. - While an example circuit topology of the low-voltage grid
clear circuit 212 and the high-voltage gridclear circuit 214 are illustrated inFIG. 3 , other circuit topologies may be used. For example, while ahigh voltage generator 316 is illustrated inFIG. 3 , other high voltage generator circuits may additionally or alternatively be used. The example high voltage controller 314 may include logic circuits and/or other control circuitry. In some examples, the high voltage controller 314 is implemented in other logic in a platform that includes theion propulsion system 200 ofFIG. 2 (e.g., in a spacecraft). -
FIG. 4 is a flowchart representative of an example method 400 to clear a short condition in a thruster grid. The example method 400 may be implemented using the low-voltage gridclear circuit 212 and the high-voltage gridclear circuit 214 ofFIGS. 2 and3 . In some examples, the method 400 is invoked when a short circuit condition is detected in a thruster grid of an ion propulsion system such as thesystem 200 ofFIG. 2 . - The example method 400 of
FIG. 4 begins by applying first energy having a first voltage (e.g., 100 V) to a grid (e.g., thegrids FIG. 3 ) (block 402). For example, the low-voltage gridclear circuit 212 may initiate a low-voltage grid clear process in response to a gridclear signal 304. The example high-voltage grid clear circuit 214 (e.g., via the high voltage controller 314) measures a first node voltage (block 404). The first node voltage may be measured, for example, at thenode 320 or at thenode 322. The high-voltage grid clear circuit 214 (e.g., via the high voltage controller 314) also measures a second node voltage (block 406). The second node voltage may be measured, for example, at thenode 324 or the node 326 (e.g., the one of thenodes node - The example high voltage controller 314 determines whether a difference between the first node voltage and the second node voltage is less than a threshold (block 408). If the difference is less than the threshold (block 408), the example high voltage controller 314 detects a failure of the first energy (e.g., from the low-voltage grid clear circuit 212) to clear the grid short condition (block 410). The high-voltage grid
clear circuit 214 applies second energy having a second voltage to the grid(s) 206, 210 (block 412). For example, the high voltage controller 314 may close the switchingelement 318 to cause thehigh voltage generator 316 to begin applying the high voltage to the grid(s) 206, 210. - The example high-voltage grid clear circuit 214 (e.g., via the high voltage controller 314) measures the first node voltage (e.g., at the
same node same node clear circuit 214 stops applying the second energy (block 422). - After stopping the second energy (block 422), or if the high voltage controller 314 determines at
block 408 that the difference between the first and second node voltages is not less than the threshold, the example low-voltage gridclear circuit 212 determines whether to stop applying the first energy (block 424). For example, the low-voltage gridclear circuit 212 may detect the state or value of the gridclear signal 304. If the low-voltage gridclear circuit 212 is to continue applying the first energy (block 424), control returns to block 402. If the low-voltage gridclear circuit 212 stops applying the first energy (block 424) or if the threshold time has elapsed (block 420), the example method 400 ends. In an example in which the threshold time elapses prior to the high-voltage gridclear circuit 214 stopping the second energy, determining the threshold time has elapsed includes stopping both the first and second energies (e.g., via the grid clear signal 304). - Although an example method is described with reference to the flowchart illustrated in
FIG. 4 , many other methods of implementing the exampleion propulsion system 200, the low-voltage gridclear circuit 212, and/or the high-voltage gridclear circuit 214 may alternatively be used. For example, the order of execution of the blocks may be changed, and/or some of the blocks described may be changed, eliminated, or combined. - Examples of the disclosure may be described in the context of a platform manufacturing and
service method 500 as shown inFIG. 5 and aplatform 600, such as spacecraft, as shown inFIG. 6 . During pre-production, theexample method 500 may include specification and design (block 502) of the platform 600 (e.g., a spacecraft), such as the placement(s) and/or design(s) of theexample power supplies 202, theexample thruster 204, the example low-voltage gridclear circuit 212, and/or the high-voltage gridclear circuit 214. Preproduction may further include material procurement (block 504). During production, component and subassembly manufacturing (block 506) and system integration (block 508) of the platform 600 (e.g., a spacecraft) takes place. During component and subassembly manufacturing (block 506) and/or system integration (block 508), theexample power supplies 202, theexample thruster 204, the example low-voltage gridclear circuit 212, and/or the high-voltage gridclear circuit 214 may be attached (e.g., affixed) to structural locations. Thereafter, the platform 600 (e.g., a spacecraft) may go through certification and delivery (block 510) in order to be placed in service (block 512). While in service by a customer, the platform 600 (e.g., a spacecraft) is scheduled for routine maintenance and service (block 514), which may also include modification, reconfiguration, refurbishment, etc. - Each of the operations of the
example method 500 may be performed or carried out by a system integrator, a third party, and/or an operator (e.g., a customer). For the purposes of this description, a system integrator may include without limitation any number of platform (e.g., aircraft) manufacturers and major-system subcontractors; a third party may include without limitation any number of venders, subcontractors, and suppliers; and an operator may be an airline, leasing company, military entity, service organization, and so on. - As shown in
FIG. 6 , the platform 600 (e.g., spacecraft) produced byexample method 500 may include aframe 602 with a plurality ofsystems 604 and an interior 606. Examples of high-level systems 604 include one or more of apropulsion system 608, anelectrical system 610, ahydraulic system 612, and anenvironmental system 614. The example methods and apparatus disclosed herein may be integrated into the example systems 608-614 to provide clearing of grid short circuits. Any number of other systems may be included. - Apparatus and methods embodied herein may be employed during any one or more of the stages of the production and
service method 500. For example, components or subassemblies corresponding toproduction process 506 may be fabricated or manufactured in a manner similar to components or subassemblies produced while the platform 600 (e.g., spacecraft) is inservice 512. Also, one or more apparatus embodiments, method embodiments, or a combination thereof may be implemented during the production stages 506 and 508, for example, by substantially expediting assembly of or reducing the cost of a platform 600 (e.g., spacecraft). Similarly, one or more of apparatus embodiments, method embodiments, or a combination thereof may be utilized while the platform 600 (e.g., spacecraft) is inservice 512, for example and without limitation, to maintenance andservice 514. - Although certain example apparatus and methods have been described herein, the scope of coverage of this disclosure is not limited thereto. On the contrary, this disclosure covers all apparatus and methods fairly falling within the scope of the appended claims.
Claims (13)
- An ion propulsion system (200), comprising:a plurality of adjacent ion propulsion system thruster grids (206, 208, 210) including outer grids;a low voltage grid clear circuit (212) configured to apply first energy to the outer grids at a first voltage; anda high voltage grid clear circuit (214) configured to apply second energy to the outer grids at a second voltage higher than the first voltage,
- The ion propulsion system as defined in claim 1, wherein the high voltage grid clear circuit (214) is configured to detect a short circuit condition in the grids by:measuring a first node voltage in the low voltage grid clear circuit (212); andcomparing the first node voltage to a threshold.
- The ion propulsion system as defined in claim 2, wherein the high voltage grid clear circuit (2124) is configured to detect a failure of the first energy to clear the short circuit condition of the grids by:measuring a second node voltage in the low voltage grid clear circuit (212) at a different node than the first node voltage; andcomparing a difference between the second node voltage and the first node voltage to a threshold, the high voltage grid clear circuit (214) configured to apply the second energy in response to detecting the failure.
- The ion propulsion system as defined in claim 1, wherein the high voltage grid clear circuit (214) is configured to:detect that the low voltage grid clear circuit (212) is applying the first energy to the grids: andstop applying the second energy in response to detecting that the low voltage grid clear circuit (212) is applying the first energy.
- The ion propulsion system as defined in claim 4, wherein the high voltage grid clear circuit (214) is configured to detect that the low voltage grid clear circuit (212) is applying the first energy by detecting a voltage drop in the low voltage grid clear circuit (212).
- The ion propulsion system as defined in claim 1, wherein the second voltage is to cause an arc between the grids.
- The ion propulsion system as defined in claim 6, wherein the first energy at the first voltage is not sufficient to cause an arc between the grids and the second grid.
- A method for operating the ion propulsion system (200) of claim 1, comprising:detecting a first grid clear process comprising applying the first voltage to the outer grids; andapplying a second grid clear process comprising applying the second voltage higher than the first voltage to the outer grids.
- A method as defined in claim 8, wherein detecting the first grid clear process comprises measuring a first node voltage at a first node.
- A method as defined in claim 9, further comprising:measuring a second node voltage at a second node;comparing a difference between the second node voltage and the first node voltage to a threshold; anddetecting a failure of the first grid clear process to clear a condition in the grids based on the comparison, wherein applying the second grid clear process is in response to detecting the failure.
- A method as defined in claim 8, wherein the second grid clear process comprises applying energy at the second voltage to the grids to cause an electrical arc between the grids.
- A method as defined in claim 8, further comprising:while applying the second grid clear process, detecting a current being applied via the first grid clear process; andstopping the second grid clear process in response to detecting the current.
- A method as defined in claim 8, wherein applying the second grid clear process is performed while applying the first grid clear process.
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US13/655,138 US9038364B2 (en) | 2012-10-18 | 2012-10-18 | Thruster grid clear circuits and methods to clear thruster grids |
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US9038364B2 (en) | 2012-10-18 | 2015-05-26 | The Boeing Company | Thruster grid clear circuits and methods to clear thruster grids |
WO2017196622A2 (en) | 2016-05-11 | 2017-11-16 | Veeco Instruments Inc. | Ion beam materials processing system with grid short clearing system for gridded ion beam source |
SG10201705059TA (en) | 2016-06-24 | 2018-01-30 | Veeco Instr Inc | Enhanced cathodic arc source for arc plasma deposition |
GB201811533D0 (en) | 2018-07-13 | 2018-08-29 | Ge Aviat Systems Ltd | Method and circuit for detecting an arc fault |
CA3102563A1 (en) * | 2020-12-13 | 2022-06-13 | Sarantis L. Randell | Ionic propulsive grid topology emitter combination |
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US6507142B1 (en) * | 2000-07-26 | 2003-01-14 | Aerojet-General Corporation | Plume shield for ion accelerators |
US6617549B2 (en) * | 2001-12-06 | 2003-09-09 | Illinois Tool Works Inc. | Method and apparatus for welding with restrike |
US6786035B2 (en) | 2002-07-22 | 2004-09-07 | The Boeing Company | Ion thruster grid clear |
US7270300B2 (en) * | 2003-10-30 | 2007-09-18 | Northrop Grumman Corporation | System and method for an ambient atmosphere ion thruster |
CN100585840C (en) * | 2008-10-23 | 2010-01-27 | äøęµ·äŗ¤éå¤§å¦ | Multi-stage type ion fluidic device and method |
FR2945842B1 (en) * | 2009-05-20 | 2011-07-01 | Snecma | PLASMA PROPELLER WITH HALL EFFECT. |
US9038364B2 (en) | 2012-10-18 | 2015-05-26 | The Boeing Company | Thruster grid clear circuits and methods to clear thruster grids |
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CN103769392A (en) | 2014-05-07 |
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